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Trace-element abundances in the shallow lithospheric mantle of the North Atlantic Craton margin: Implications for melting and metasomatism beneath Northern Scotland

Published online by Cambridge University Press:  02 January 2018

Hannah S. R. Hughes ,
Iain McDonald ,
John W. Faithfull ,
Brian G. J. Upton  and
Hilary Downes
Hannah S. R. Hughes*
Affiliation:
School of Earth and Ocean Sciences, Cardiff University, Main Building, Cardiff CF10 3AT, UK
Iain McDonald
Affiliation:
School of Earth and Ocean Sciences, Cardiff University, Main Building, Cardiff CF10 3AT, UK
John W. Faithfull
Affiliation:
Hunterian Museum and Art Gallery, University of Glasgow, Glasgow G12 8QQ, UK
Brian G. J. Upton
Affiliation:
School of Geosciences, University of Edinburgh, Edinburgh EH9 3JW, UK
Hilary Downes
Affiliation:
Department of Earth and Planetary Sciences, Birkbeck University of London, Malet Street, LondonWC1E 7HX, UK
*
*E-mail: [email protected]
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Abstract

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Bulk rock geochemistry and major- and trace-element compositions of clinopyroxene have been determined for three suites of peridotitic mantle xenoliths from the North Atlantic Craton (NAC) in northern Scotland, to establish the magmatic and metasomatic history of subcontinental lithospheric mantle (SCLM) below this region. Spinel lherzolites from the southernmost locality (Streap Com'laidh) have non-NAC mantle compositions, while the two northern xenolith suites (Loch Roag and Rinibar) are derived from the thinned NAC marginal keel. Clinopyroxene compositions have characteristic trace-element signatures which show both 'primary' and 'metasomatic' origins. We use Zr and Hf abundances to identify ancient cryptic refertilization in 'primary' clinopyroxenes. We suggest that Loch Roag and Rinibar peridotite xenoliths represent an ancient Archaean-Palaeoproterozoic SCLM with original depleted cratonic signatures which were overprinted by metasomatism around the time of intrusion of the Scourie Dyke Swarm (∼2.4 Ga). This SCLM keel was preserved during Caledonian orogenesis, although some addition of material and/or metasomatism probably also occurred, as recorded by Rinibar xenoliths. Rinibar and Streap xenoliths were entrained in Permo-Carboniferous magmas and thus were isolated from the SCLM ∼200 Ma before Loch Roag xenoliths (in an Eocene dyke). Crucially, despite their geographical location, lithospheric mantle peridotite samples from Loch Roag show no evidence of recent melting or refertilization during the Palaeogene opening of the Atlantic.

Keywords

North Atlantic Cratonspinel lherzolitexenolithREEclinopyroxene
Type
Research Article
Information
Mineralogical Magazine , Volume 79 , Issue 4 , August 2015 , pp. 877 - 907
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2015 This is an Open Access article, distributed under the terms of the Creative Commons Attribution license. (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2015

Footnotes

†

Present address: School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa

*

This paper is published as part of a special set in Mineralogical Magazine, Volume 79(4), 2015, arising out of the March 2014 NAC Conference on the North Atlantic Craton.

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